For co-existence between systems along with the rapid development of wireless communication technology, each wireless communication system should secure and maintain its own frequency band. However, as almost of all substantially available frequency bands have been allocated, the lack of frequency resources for a new wireless communication system has become a challenging issue. Accordingly, frequency bands ranging from a few Hz to hundreds of GHz are all occupied and thus little frequency remains for additional use.
To solve the lack of radio frequency resources, one technique under recent consideration is CR. It is difficult to allocate a new frequency to a new communication service under the current fixed frequency allocation policy due to limited spectrum resources. However, it has been revealed that the use rates of the current allocated frequencies are very low. In this context, dynamic and opportunistic spectrum access techniques have been studied.
FIG. 1 illustrates a CR communication system according to the related art.
Referring to FIG. 1, when a licensed Primary User (PU) does not use a channel, an unlicensed Secondary User (SU) may use the channel in the CR communication system. CR is based on Software Defined Radio (SDR). SDR enables a transceiver to tune to an intended spectrum band by changing a software parameter without any hardware modification. In an initial stage, a centralized CR system such as one conforming to Institute of Electrical and Electronics Engineers (IEEE) 802.22 was designed by SDR in a cellular network. A new CR system has also been developed for an ad-hoc network. A pair of terminals can transmit and receive data during one frame interval by a MAC protocol in a conventional CR system designed for an ad-hoc network.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.